Devices configured to transmit engine sound from the engine compartment of a motor vehicle into the passenger compartment are known. In one known configuration a sound transmission device includes a flexible tube or pipe in which one end is connected into the air intake tract of the engine and an opposing end is positioned near or extending through the firewall into the passenger compartment.
As a drive unit, modern motor vehicles have internal combustion engines that operate very smoothly so that the engine operating sound may be barely audible within the interior of the motor vehicle. As designs evolve to address lower CO2 emissions and improved fuel economy, smaller engines are utilized together with lighter weight vehicle designs. The reduced operating sound of the internal combustion engine may be further obscured by other secondary noises such as road noises, vehicle HVAC systems, etc.
Under certain circumstances it can be desirable to transmit the operating sound of the internal combustion engine to the interior of the motor vehicle. Engine sound may be channeled through the sound transmission device to provide a “sporty” engine sound experience to the driver and passengers. In some cases the sound output of the sound transmission device is relatively low in volume with the result that it is sometimes desirable to extend the sound transmission device tube into the vehicle interior from the engine compartment to thereby improve the transmitted engine sound amplitude level for an improved driver experience.
It is known to provide a flexible diaphragm in the sound transmission tube to provide airflow isolation, thereby preventing airflow through the sound transmission tube. Even if the sound tube is not extended into the passenger compartment, it is undesirable to permit airflow back into the engine air intake tract through a sound transmission tube for which the purpose is strictly to conduct sound. This is especially undesirable if the sound tube is connected to the clean side of the air filter as any airflow through the tube would be introduced as unfiltered air into the air intake tract.
It is known to provide tuning of a transmitted sound spectrum in a vehicle sound transmission device by the addition of a quarter wave tuner or a resonator chamber in the sound transmission tubing. A quarter wave tuner is useful to attenuate or cancel a selected transmitted sound frequency. The quarter wave tuner may be positioned and connected to the sound transmission tubing so as to extend outwards from the tubing in a branch configuration, typically (although not necessarily) at about 90 degrees relative to the axis of the sound transmission tubing. Alternately, when it is desired to amplify a selected transmitted sound frequency then an inline resonator chamber may be provided in the sound transmission tubing. If the inline resonator is configured with a duct length L, then the amplified sound wavelength will be a function of L/2. The use of quarter wave tuners and inline resonators, alone or in combination, permit the transmitted sound to be tailored using only passive devices rather than by the application of more expensive and complicated active electronic devices.
Published U.S. patent application Ser. No. 12/061,703 discloses a device for noise transmission in a motor vehicle. In this device sound is transmitted along a transmission line having an enlarged mouth at one end and a diaphragm fitted to close off the mouth. A protective device is fitted at the end to protect the diaphragm.
U.S. Pat. No. 6,600,408 B1 discloses a device for sound transmission for a motor vehicle. In this device, the sound is transmitted along a pipe conduit and a chamber in which a diaphragm is arranged toward the interior of the motor vehicle. The chamber that surrounds the diaphragm is comprised of several assembled parts.
German patent publication DE 101 16 169 A1 discloses a resonator chamber in which the diaphragm is arranged.
German patent DE 44 35 296 discloses a diaphragm for noise transmission in a motor vehicle in which the diaphragm is clamped in a holder.
U.S. published patent application 2006/0283658 A1 discloses a system for noise increase of an intake system of a motor vehicle. Various possibilities of noise introduction into the interior of the motor vehicle are illustrated wherein the diaphragm is arranged in a pipe conduit for noise transmission.
In the German publication DE 199 30 025 A1 a sound transmission body is illustrated in which the diaphragm is clamped between two transmission members.